MKPolyline strange rendering related with zooming in MapKit

Question

I have very simple View Controller to demonstrate this strange rendering behavior of MKPolyline. Nothing special just normal api calls. ``` import UIKit import MapKit class ViewController: UIViewController, MKMapViewDelegate { @IBOutlet weak var map: MKMapView! override func viewDidLoad() { super.viewDidLoad() map.delegate = self } override func viewDidAppear(_ animated: Bool) { super.viewDidAppear(animated) let p1 = CLLocationCoordinate2D(latitude: 51, longitude: 13) var coords = [ p1, CLLocationCoordinate2D(latitude: 51.1, longitude: 13), CLLocationCoordinate2D(latitude: 51.2, longitude: 13), CLLocationCoordinate2D(latitude: 51.3, longitude: 13) ] let polyline = MKPolyline(coordinates: &coords, count: coords.count) map.addOverlays([polyline], level: .aboveRoads) let cam = MKMapCamera(lookingAtCenter: p1, fromDistance: 1000, pitch: 45, heading: 0) map.setCamera(cam, animated: true) } func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -> MKOverlayRenderer { let r = MKP…

Accepted Answer

Swift 3 solution :

Create a subclass of MKPolylineRenderer

```
class CustomPolyline: MKPolylineRenderer {

override func applyStrokeProperties(to context: CGContext, atZoomScale zoomScale: MKZoomScale) {
        super.applyStrokeProperties(to: context, atZoomScale: zoomScale)
        UIGraphicsPushContext(context)
        if let ctx = UIGraphicsGetCurrentContext() {
            ctx.setLineWidth(self.lineWidth)
        }
    }
}
```

Then use it in your rendererFor MapKit delegate :

```
func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -> MKOverlayRenderer {
        let renderer = CustomPolyline(overlay: overlay)
        renderer.strokeColor = UIColor.red
        renderer.lineWidth = 100
        return renderer
}
```

Your polylines won't re-render after zooming thus avoiding the artifacts

MKPolyline strange rendering related with zooming in MapKit

Solution

Problem

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